The fediverse is the network of federated decentralized social media using activitypub to connect. Lemmy (the software on which chapo.chat is based) will be in some months part of this network.
What do you think about fediverse ? Are some of you using Mastodon as a twitter replacement ?
Yes crossplay is a good example of federation, when it comes to identity management. Each network (xbox live, PSN, PC) has their own identity providers (steam, xbox, psn) and crossplay allows people from different networks to play on the same game session.
This is seperate from the discussion around interoperability, meaning the sharing of gamestate between different versions of the same game, running on these different platforms. It's an important distinction, that I think sometimes people take the interoperability concept and roll it up into the term federation.